13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- s Ic 2 K , 1 ν EG = − (11) wherе Gs is the threshold fracture energy. Formula (11) allows determining the value of К1с by means of critical specific fracture energy Gs. Fig. 5. Loading diagrams of the VТ6-alloy (а) and commercial titanium VТ1-0 (b) with UFG structure. Values of crack resistance characteristics for the studied materials are presented in Tab. 1. It is seen that specific fracture energies of the VТ6-alloy in CG and UFG states differ significantly. Dimension of the Gs characteristics is energy per unit area. However, this value is not a surface energy of the material. The last one is several orders of magnitude smaller than fracture energy Gs. Thus, surface energy of titanium is equal to 1.7 J/m2 [12], at the same time, energy fracture value of commercial titanium, according to our calculations, is Gs = 27.82 kJ/m2. Agreement in values of Gs and surface energy will be observed only in case of totally brittle fracture. A colossal difference is caused by plastic strain processes intensively developing in metals and alloys that lead to essential change in shape and strain-stress state locally at the crack tip. Table 1. Mechanical characteristics of commercial titanium VТ1-0 and VТ6 Material λр/λе Gs, kJ/m2 КIс, MPa/m1/2 Е, GPa VТ1-0 UFG 0.11 27.82 56.37 113 VТ1-0 CG 111 VТ6 UFG 0.11 31.48 63.2 114 VТ6 CG 0.37 53.00 90.8 110 According to equation (10), the values of λе are equal to 1.07 and 1.914 mm for VТ6 and VТ1-0, respectively. These values appeared smaller than experimentally measured displacement values of load application points λ, i.e. λ is equal to 1.21 mm for VТ6 and λ makes 2.12 mm for VТ1-0. Difference between measured and calculated values is caused by additional contribution of λр plastic strain into displacement of load application points, i.e. λр is equal to 0.14 mm for VТ6 and λр is equal
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